1. Field of the Invention
The present invention relates to an image generating apparatus and method, in particular an image generating apparatus and method that can quickly generate an image having a natural depth of field and can control the depth of field.
This application is based on patent number Hei 9-144024 and Hei 9-217725 filed in Japan, the contents of which are incorporated herein by reference.
2. Description of Related Art
Conventionally, there are two methods for achieving a realistic depth of field when generating an image by computer graphics: (1) applying a defocus filter to defocus a picture whose entire area focused when generated by conventional methods, (see Potmesil, Michael, et al. "A Lens and Aperture Camera Model for Synthetic Image Generation", Computer Graphics, vol. 17, pp. 137-145, 1981.), and (2) applying distributed ray tracing (see Cook, R. L. et al. "Distributed Ray Tracing", Computer Graphics, vol. 118, pp. 137-145, 1984). One of the most important characteristics which a natural depth of field has when actually seen is that the image of a physical object in front of the focussed distance is defocused and, at the same time, is transparent at the edge. In the first method mentioned above, because a defocused picture is generated by removing all hidden surfaces, no matter how much this kind of object in front of the focussed distance is defocused, it is fundamentally impossible to make the objects in front of it appear transparent, and as a result, there is the problem that an unnatural picture is generated. Additionally, in the second method mentioned above, while this kind of problem basically does not occur, its basis is distributed ray tracing which by nature is very time consuming, and it is necessary to trace at least tens of rays, giving rise to the problem that a great amount of time is necessary to generate the desired image.
Additionally, generally no matter what method is used, in order to make a composite after a plurality of images has been generated, by the conventional technology the composite borders must be made distinct, and the objects composited in front must be generated in focus, and the edges of the image of this object must be made distinct. If the composited objects in front are to be defocused, they must be composited with skilled manual work, and therefore, the amount of work for moving images is extremely large. In order to avoid this, generally when photographing objects beforehand, they all had to be photographed from front to back so that they were in focus (below called "pan-focus"), and the limitations in conditions for photography were very restrictive.